急性胃肠炎时,引起呕吐的病因为A.反射性呕吐 B.喷射性呕吐 C.中枢性呕吐 D.前

题型:单项选择题

问题:

急性胃肠炎时,引起呕吐的病因为

A.反射性呕吐

B.喷射性呕吐

C.中枢性呕吐

D.前庭障碍性呕吐

E.神经官能性呕吐

考点:专升本考试医学综合专升本医学综合
题型:单项选择题

阅读下面的现代文,完成第7~10题。
寻找最有效、最经济的汽车燃料
当一些研究人员集中精力研究汽车并改进汽车系统和材料时,另一些人的研究重点则放在汽车的燃料上。至少在一定情境下,改进汽车和提炼燃料是携手并进的。在研制出催化转化器之后,石油工业必须使汽油变成无铅汽油。含铅汽油排放的废气中有铅,使转化器中的金属涂上一层膜,导致这些金属失效。由于铅已与癌症联系起来并能引起儿童神经系统损伤,因此无铅汽油是针对汽车污染的一项重要发展。
研究人员继续寻找改善汽油的办法。提炼原油以产生汽油涉及给石油加热并在石油挥发过程中提取各种碳氢化合物。有一些碳氢化合物是容易挥发的轻量分子,另一些碳氢化合物则重一些,它们有形成沉积物和微粒的趋势,并可能引起癌症。
石油公司通过多使用重量等级居中的碳氢化合物——既不很轻也不很重的碳氢化合物,就能创造出污染较少的汽油。提炼厂也能分解或“裂化”较重的碳氢化合物以产生较轻的化合物。一些汽油添加剂在其结构中含有氧原子。这有助于促使燃料燃烧更完全。
研究人员也在调查除汽油之外的其他燃料。甲醇排放的污染物数量较少,这些污染物通常与汽油燃烧有关。但是甲醇的潜能比汽油少,而且甲醇更难点燃。甲醇也能腐蚀许多金属。最后,甲醇产生一种刺激眼睛、鼻子和咽喉的有害化合物,被认为能引起癌症。从积极方面来说,甲醇比汽油燃烧得更完全,在与15%的汽油混合在一起形成一种叫M-85的燃料时,这种新燃料的启动性能令人满意。一种使用“灵活燃料”的引擎既能烧汽油也能烧甲醇,或者同时烧两种燃料。特殊传感器能决定使用哪一种燃料,并能把这个信息传达到中央电脑系统。
天然气是专家们认为能代替汽油的另一种储量丰富的燃料。天然气主要由甲烷气构成,比汽油便宜,也比汽油清洁得多。这种燃料的主要缺点是,不像汽油和甲醇,天然气在正常的气温和气压下无法以液态存在。天然气必须装在压力罐中,或者液态时要装在绝缘罐中——这是消费者可能拒绝的汽车设计之外的陌生附加物。加注天然气最多可能需要几个小时的时间。
一些科学家对把氢气作为一种未来的燃料感兴趣。氢燃烧比其他燃料燃烧都更清洁,而且容易生产。但是在氢气能广泛用于汽车之前,必须先解决复杂的技术问题。
电车安静,实际不排放任何废气。但是,电车用以获取能源的电池通常含有有害的化学物质。在电池被抛弃后这些化学物质就变成了污染物。由于电池供应的能量不如汽油燃烧产生的能量大,因此今天的电车不可能像汽油驱动的车辆跑得那样远或那样快。此外,电池必须经常充电,充电所需的能源来自发电厂,而发电厂本身也是污染源。尽管如此,在像加利福尼亚这样一些已制定零排放法的地区,电车是满足零排放要求的可能选择。
设法使汽车更清洁的继续不断的探索是对工程师以及化学家、材料科学家和技师提出的严峻挑战。我们的夙愿是维护汽车给我们发达的世界带来的行动自由。而目前这种广泛探索同我们的夙愿一起,反映出我们对环境所给予的新的和强烈的关注。

下面最干净的燃料是( )

A.汽油

B.甲醇

C.氢气

D.天然气

题型:单项选择题

How difficult change is depends a lot on your attitude towards it and your resistance to it. Your attitude to change can make the whole transformation process much easier.

Imagine change as a pair of shoes and this will help you understand change and how it works. I am sure that you have ever had a comfortable pair of shoes in your life. A pair of shoes is so comfortable that you really don’t want to get rid of them.

You know you need a new pair, and may even have them, but you don’t want to wear them because you are comfortable with your current pair. Besides, the new pair may hurt your feet, give you blisters(水疱) or be awkward to wear to start with. So, you resist the new shoes. However, you know that this new pair would be much better for your feet, and after the initial discomfort they would probably be even more comfortable, yet you still resist.

Do you know I’m doing this now? I’m wearing my comfortable shoes and they feel good. They have a hole in each heel, and the sole is starting to fall off, but I’m persisting in wearing them.

This describes change exactly; change of our habits, change of our thought patterns. We stick with the old patterns because they are comfortable. Yet once we get over the initial pain of the transformation, the new pattern will be comfortable and feel good until the time comes when we need another new pair of shoes.

小题1:Why do people prefer old shoes to new ones?

A.They have much emotion in the old ones.

B.They are more comfortable.

C.New shoes always harm the feet.

D.They look better than the new ones.小题2: According to the passage, we know that people ______.

A.don’t realize the benefit of the new shoes very well

B.are positive and open-minded to accept new things

C.actually know the change will finally be good for them

D.don’t accept new patterns because they are not good小题3: What can be inferred from the passage?

A.Once we form a habit, it’s difficult to change it.

B.Most people pay more attention to the future life.

C.One’s attitude towards something is usually traditional.

D.The more often we change, the better our life will be.

题型:单项选择题

在关系数据库系统中,为了简化用户的查询操作,而又不增加数据的存储空间,常用的方法是创建( )。

A.另一个表(Tabl

B.游标(Curso

C.视图(Vie

D.索引(Inde

题型:单项选择题

民法:法律:法官

A.榕树:植物:园丁
B.母牛:奶牛:牧民
C.太阳:月亮:银河系
D.学生:中学生:教师

题型:单项选择题

曲轴主轴颈或轴承磨损严重,间隙过大,将造成()。

A.机油压力过高

B.机油压力过低

C.气缸上部有金属敲击声

D.突然加速或减速时,出现低沉、钝哑的“嘡嘡”声

E.单缸断火时响声无变化,相邻两缸断火响声减弱或消失

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